|NEC Questions for EC&M Magazine
By Mike Holt for EC&M
Q1. A 1200A main breaker is fed with 3 sets of 500 kcmil THHN
conductors. Is this installation legal?
A1. No. Where the overcurrent
device is rated over 800 amperes, the conductors must have an ampacity of not
less than the rating of overcurrent protection device [240.4(C)]. It's true that
the total ampacity of 3 sets of 500 kcmil THHN conductors at 90°C is greater
than 1200A (430A x 3 = 1290A), but the conductors must be size based on the 75°C
column of Table 310.16 in accordance with 110.14(C)(1)(b). At 75°C, the 500
kcmil THHN are only rated 380A x 3 = 1140A, therefore 600 kcmil conductors must
Q2. I have a 1200A service and I want to supply it with 3 sets
of 500 kcmil THHN conductors. I would like to set a splice box near the
termination point and splice the 500 kcmil conductors to 600 kcmil THHN
conductors. Is there anything wrong with this picture?
A2. This is fine
if the splicing fittings are rated for 90°C and they are installed in accordance
with 110.14 of the NEC.
Q3. I am moving a pool pump motor and the
inspector wants me to splice the 8 AWG bonding jumper by exothermic welding or
an irreversible compression type-connector listed. Is he correct?
No. Connections of the 8 AWG pool bonding conductor must be made by exothermic
welding or by pressure connectors or clamps that are labeled as being suitable
for the purpose [680.26(C)].
Q4. My question is about the new trend for
residential, under the counter, washer and dryer installations. I don't think
the cord is accessible to be used as a disconnecting means when the appliance is
installed? Am I correct in my interpretation of the term "accessible?"
A4. No. Accessible means capable of being removed or exposed without
damaging the building structure or finish or not permanently closed in by the
structure or finish of the building . So the installation is fine, see
Q5. The 2002 NEC states that all branch circuits that supply
125V, 15A or 20A outlets in dwelling unit bedrooms be AFCI protected. Would this
apply to smoke detectors and wall air conditioning units connected to a 125V,
15A or 20A circuit? Is AFCI protection required for switches located in the
bedroom that controls a lighting outlet in another space?
protection is required for all 125V, 15A and 20A outlets, and this would include
the outlet for smoke detectors as well as wall air conditioners. I'm not sure if
the AFCI breaker will nuisance trip when it supplies large inductive reactive
loads such as air conditioning equipment on dedicated circuits. Time will tell.
About the switches, if the switch controls utilization equipment in the
bedroom, then it will be AFCI protected. However, if the switch operates
lighting outlets for outdoor luminaire, closets or other loads not terminated in
bedroom space then AFCI protection is not NEC required, because a switch is not
considered an outlet*.
*According to Article 100, an outlet is defined
as a point on the wiring system at which current is taken to supply equipment
that utilizes electric energy for electronic, electromechanical, chemical,
heating, lighting, or similar purposes . This would include a receptacle
outlet, a lighting outlet, but not a switch.
Q6. Is ground-fault
protection of equipment of the type specified in 230.95 required for a 2000A,
480/277V, three-phase, 4-wire generator main breaker?
A6. The general
requirement is that ground-fault protection of equipment must be provided for
480/277V electrical services and feeders disconnect rated 1000 amperes or more
[215.10 and 230.95]. However, such protection is not required for emergency
standby power disconnects [700.26] or required standby power disconnects
Q7. During an infrared inspection, we found a 400A breaker
that had nine conductors per phase on the load side, consisting of 10 AWG, 8 AWG
and 1/0 AWG conductors. The customer claimed it was legal per the 10' tap rule.
A7. This installation does not violation of the 10 ft feeder tap rule,
assuming all of the requirements contained in 240.21(B)(1) are followed. But,
110.14(A) only permits one conductor per terminal unless the terminal is so
identified. Naturally, there are no 400A breakers identified to be use with nine
Q8. Most dwellings in our area have plastic underground
water pipes supplying the house. The internal water piping is changed to copper
inside the house. My inspector requires that we bond the interior metal water
pipe system at the water heater. But I fee that 250.52(A)(1) says that the
bonding connection must not be made more than 5' from the point of entry. I say
it is a violation to make this connection further than 5 ft from the point of
entry. Am I right?
A8. No. The 5 ft from the point of entry rule
contained in 250.52(A)(1) applies when the metal water pipe is used as a
conductor to interconnect electrodes that are part of the grounding electrode
system. This rule does not apply to the bonding requirements of 250.104, which
only limits the connection to an accessible location.
Q9. What is the
maximum height of an exit sign?
A9. There is no minimum or maximum
height in the NEC. But Life Safety Code 101 specifies that floor proximity exit
lights, if required by local codes be located with the bottom between 6 and 8
inches above the floor. In addition, NFPA 5000 section 126.96.36.199 states that
"Egress markings must be located at a vertical distance of not more than 6 ft 8
in (2 m), measured from above the top edge of the egress opening..."
Q10. I am working in an old home and I want to replace the existing two
prong receptacles with grounding-type (3-wire) receptacles, even though the
wiring method only has only 2 wires. What do I have to do?
According to 406.3(D)(3), where no grounding (bonding) means exists in the
outlet box, such as old 2-wire NM cable without a ground, nongrounding type
receptacles can be replaced with:
(a) Another nongrounding type
(b) A GFCI-receptacle if marked "No Equipment Ground."
grounding-type receptacle, if GFCI protected and marked "GFCI Protected" and "No
Note: GFCI protection functions properly on a 2-wire
circuit without an equipment grounding conductor, because the equipment
grounding conductor serves no purpose in the operation of the GFCI protection
CAUTION: Permission to replace nongrounding type receptacles
with GFCI-protected grounding type receptacles does not apply to new receptacle
outlets that extend from an existing ungrounded outlet box. Once you add a
receptacle outlet (branch-circuit extension), the receptacle must be of the
grounding type and it must have its grounding terminal grounded in accordance
Q11. I have a 20A branch circuit feeding modular office
furniture receptacles that are rated 15A. The inspector tells me that I must
replace the 15A receptacles with 20A receptacles. Is he right?
Where connected to a branch circuit that supplies two or more receptacles, a 15A
receptacle can be installed and protected by a 20A overcurrent protection device